Blood of three wishes

The story follows Sara, the world's last mermaid, who sacrifices her children and lifelong magical power one after another to save her beloved Arthur and his family. However, for his lover Amy, Arthur forces Sara to make a third wish. After she refuses, he abuses and kills her. Before dying, Sara casts a curse. Eventually, Amy's deception is exposed, and Arthur, along with his mother, his lover and David, suffers terrible retribution, ending up with a ruined family and miserable fates.